Controlled Growth of Disordered Si Nanowire Arrays at Room Temperature for Self-Cleaning and Anti-Reflection Applications
Date Issued
2009
Date
2009
Author(s)
Dai, Yu-An
Abstract
Various methods to synthesize Si nanowire arrays (Si NWAs) have been developed. Very recently, Si NWAs have been widely utilized for the device applications, such as antireflection (AR) or self-cleaning. The reduction of surface reflection and the super-hydrophobic effect are desirable to apply for solar cells. To the best of our knowledge, there are no reports on the AR and super-hydrophobic effect on the structural properties, such as morphology and density of Si NWAs.n this work, the galvanic wet etching was adopted to fabricate disordered single-crystalline Si NWAs at room temperature in HF/AgNO3 solution. The length and density of Si NWAs could be controlled by adjusting the etching time, and the growth rate is estimated to be linear behavior. An average total reflectance 1~2% over a wide range of wavelength showed the broadband AR characteristics of Si NWAs. Angular dependent of spectral measurements of the Si NWAs are insensitive to TE and TM polarization, demonstrating omnidirectional AR characteristics. Excellent AR behavior is due to the gradient refractive index profile of Si NWAs. The effective index of Si NWAs was calculated by the effective medium theory. Morphology-dependent Brewster angle was observed. Moreover, the self-cleaning effect was examined by the basic contact angle and hysteresis theories. According to the Cassie’s theory, the calculation results agree well with the measured data, showing super-hydrophobic effect. Building self-cleaning feature into a broadband and omnidirectional AR coating can keep contamination to a minimum so that long-term performance of optoelectronic device can be maintained.
Subjects
Silicon nanowire
antireflection
self-cleaning
contact angle
effect medium theory
Type
thesis
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